Protein Engineering of Albebetin, A de Novo Protein with a Predesigned Three-Dimensional Structure

Abstract

The design of de novo proteins which ensures the desirable three-dimensional (3-D) structures is the best way to test our understanding of the principles of protein structure and protein folding. The first successful engineering of a de novo protein, namely four-helix bundle, has been reported seven years ago (Regan and DeGrado, 1988) and then a number of attempts have been made in this direction during the past years (for a recent review see Sander, 1994). Most of the designed structures mimicked the 3-D structures of some natural proteins. In 1988 four of us have reported a design of a de novo protein albebetin (Figure 1) with a predetermined 3-D fold consisting of a four-stranded antiparallel β-sheet with one side screened by two α-helices (Finkelstein et al., 1988). This fold does not contradict any structural rule but has been never observed up to now in natural proteins. It consists of two identical αββ units, therefore we have called our de novo protein albebetin. We have expressed albebetin in a cell-free translational system and in E.coli and investigated it by various physical and chemical techniques (Dolgikh et al., 1991, 1992; Fedorov et al., 1992; Chemeris et al., 1994). It has been shown that the de novo protein is relatively stable and nearly as compact as natural proteins, it unfolds cooperatively at high urea concentrations and possess structural features of a definite structure consistent with the predesigned one. An eight amino acids biologically active human interferon fragment was attached to albebetin in order to obtain a de novo protein with a grafted biological function (Dolgikh et al., 1993).